Various autonomic responses (electrodermal activity, heart rate, pulse volume) as well as muscle tension are being studied in learning paradigms with human subjects. Conditioning of these physiological responses is observed as a function of cognitive and information variables like certainty about occurrence of noxious stimulation. One series of projects compares methods for producing conditioned inhibition of such responses as well as the interaction of behavior which occurs on presentation of both excitatory and inhibitory stimuli in a summation paradigm. "Random-contingency stimuli" are being used in an effort to define the zero reference point on a scale of learned excitation-inhibition. The informational studies manipulate event, time, and quality certainty of prediction within series of stimulus presentations. Special attention is being paid to the influence of the predicitve certainty information upon responses in anticipation of strong stimulation as well as responses to the strong stimuli themselves. Magnitude of autonomic reaction is compared to psychophysical judgments of subjective intensity of the stimuli.